The present invention generally relates to a computer system of virtual storage type. More particularly, the invention is concerned with a computer system in which data sets are resident in a virtual storage.
At present, most of the computers use a virtual storage system having a configuration in which a main storage is divided into pages so that fragmentation can be avoided in the main storage with a view to enhancing effective utilization of the main storage while increasing the apparent capacity thereof.
At the present state of the virtual storage computer system, the virtual storage is destined to hold therein only a program. There is not yet available the technique allowing data to be stored in the virtual storage in addition to the program. Consequently, upon accessing the data, it is required to make access to a disk storage unit through the medium of a channel unit by issuing an I/O (input/output) instruction. To this end, a corresponding channel program has to be made available in the main storage. The channel program and the input/ output data area are ordinarily given in terms of virtual addresses. The channel unit performs a data transaction directly with the main storage (the area indicated by the real addresses). Consequently, address translation has to be performed for the channel program and the input/output data area (i.e. the translation of the virtual address to the real address). Further, since the input/output (I/O) operation can not be executed in case the area of concern is paged-out when the channel program and the input/output area are referenced, it becomes necessary to fix the page on which the area of concern exists (page fixation for inhibiting page-out). Additionally, the main storage is divided on a page basis. Accordingly, when the input/ output operation is to be performed over a range exceeding a page, an indirect data addressing word (IDAW) is added to the channel program, wherein the data I/O operation is performed over discrete pages through the control effectuated by utilizing the indirect data addressing word (IDAW). These operations provide a cause for increasing the overhead of an input/output supervisor. On the other hand, the channel program is prepared in dependence on the type of the disk unit or magnetic tape unit being employed. Consequently, when the disk unit or the magnetic tape unit is changed, alteration of the channel program is necessitated. Thus, when a new disk unit or magnetic tape unit is utilized, the data management and the input/output (I/O) supervisor must be changed correspondingly.
In the virtual storage system available at present, the main storage can be increased at maximum only to the capacity which can be indicated by the maximum virtual address. This means that the high capacity and inexpensiveness of the memory available due to progress in the hardware technology can not be made use of adequately. It is further noted that the prior art VIO (virtual I/O) technique is not designed to place the data set in the virtual memory unit but resides simply in replacement of the data set I/O by the paging I/O.
An object of the present invention is to provide a computer system in which a data set is caused to be resident in a virtual storage.
With the present invention, it is intended to make resident (i.e. reside) a virtual storage a data set such as a SAM (Sequential Access Method) data set, PAM (Partitioned Access Method) data set, VSAM (Virtual Storage Access Method) data set or the like.
Another object of the present invention is to provide a computer system in which file copy processing as well as duplicate file write processing can be effectuated effectively independent of recognition by program.
A further object of the present invention is to provide a computer system in which the magnetic disk unit and magnetic tape unit are made independent of the software.